[asveikau]

> the reading thread will now randomly return values in the wrong timezone instead, subsequent code will use it in whatever operation it is it wanted the time for, the end result will be garbage,

I really strongly disagree with how bad you seem to think this is. If you are designing your application to use the timezone and modify it at the same time, it is a totally natural consequence that you may see the previously set time zone in a timing dependent fashion. That's the nature of the beast. To "solve this" is seemingly to make that other thread capable of time travel or something. It read something before it was written, and acted on it. Reasonable!

The harmful data races are when you read intermediate results. If setting the timezone is a multi-step process, or involves manipulation on complex data structures with pointers that might be deallocated, then you are in grave danger. Seeing a previously valid result is ... I honestly don't know how you'd expect to solve it without threads being able to see the future, or some other unreasonable expectation.